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lack the hack

OpenGL texture mapping once again

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hey everybody i think i'm very close to getting texture mapping to work, but i'm having one problem. when i load a texture and display it with glTexCoord2f(), i think my color values are getting messed up. when the texture is displayed, everything becomes very dark, or everything turns black. here is the .h file i'm using for my functions of texture mapping: (this is the exact code from OpenGL Game Programming, by Dave Astle and Kevin Hawkins, the only change is the shape, and a different texture)
#ifndef texture_h
#define texture_h
#include <gl/gl.h>
#include <windows.h>
#include <cstdio>
#include <cstdlib>
#define BITMAP_ID 0x4D42
BITMAPINFOHEADER	bitmapInfoHeader;	// bitmap info header
unsigned char*		bitmapData;			// the texture data
unsigned int		texture;			// the texture object

// LoadBitmapFile
// desc: Returns a pointer to the bitmap image of the bitmap specified
//       by filename. Also returns the bitmap header information.
//		 No support for 8-bit bitmaps.
unsigned char *LoadBitmapFile(char *filename, BITMAPINFOHEADER *bitmapInfoHeader)
{
	FILE *filePtr;							// the file pointer
	BITMAPFILEHEADER	bitmapFileHeader;		// bitmap file header
	unsigned char		*bitmapImage;			// bitmap image data
	int					imageIdx = 0;		// image index counter
	unsigned char		tempRGB;				// swap variable

	// open filename in "read binary" mode
	filePtr = fopen(filename, "rb");
	if (filePtr == NULL)
		return NULL;

	// read the bitmap file header
	fread(&bitmapFileHeader, sizeof(BITMAPFILEHEADER), 1, filePtr);
	
	// verify that this is a bitmap by checking for the universal bitmap id
	if (bitmapFileHeader.bfType != BITMAP_ID)
	{
		fclose(filePtr);
		return NULL;
	}

	// read the bitmap information header
	fread(bitmapInfoHeader, sizeof(BITMAPINFOHEADER), 1, filePtr);

	// move file pointer to beginning of bitmap data
	fseek(filePtr, bitmapFileHeader.bfOffBits, SEEK_SET);

	// allocate enough memory for the bitmap image data
	bitmapImage = (unsigned char*)malloc(bitmapInfoHeader->biSizeImage);

	// verify memory allocation
	if (!bitmapImage)
	{
		free(bitmapImage);
		fclose(filePtr);
		return NULL;
	}

	// read in the bitmap image data
	fread(bitmapImage, 1, bitmapInfoHeader->biSizeImage, filePtr);
	
	// make sure bitmap image data was read
	if (bitmapImage == NULL)
	{
		fclose(filePtr);
		return NULL;
	}

	// swap the R and B values to get RGB since the bitmap color format is in BGR
	// swap the R and B values to get RGB since the bitmap color format is in BGR
	for (imageIdx = 0; imageIdx < bitmapInfoHeader->biSizeImage; imageIdx+=3)
	{
		tempRGB = bitmapImage[imageIdx];
		bitmapImage[imageIdx] = bitmapImage[imageIdx + 2];
		bitmapImage[imageIdx + 2] = tempRGB;
	}

	// close the file and return the bitmap image data
	fclose(filePtr);
	return bitmapImage;
}

void DrawGround(float xPos, float yPos, float zPos)
{
		glBegin(GL_POLYGON);
		glTexCoord2f(0.0f,0.0f);	glVertex2f(-28.0f, -40.0f);
		glTexCoord2f(0.0f,1.0f);	glVertex2f(-28.0f, -15.0f);
		glTexCoord2f(1.0f,1.0f);	glVertex2f(28.0f,-15.0f);
		glTexCoord2f(1.0f,0.0f);	glVertex2f(28.0f,-40.0f);
		glEnd();
}
void Initialize()
{
	glEnable(GL_TEXTURE_2D);					// enable 2D texturing
	// load our bitmap file
	bitmapData = LoadBitmapFile("sand128.bmp", &bitmapInfoHeader);

	glGenTextures(1, &texture);                  // generate texture object
	glBindTexture(GL_TEXTURE_2D, texture);       // enable our texture object
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

     // generate the texture image
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, bitmapInfoHeader.biWidth,
				 bitmapInfoHeader.biHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, bitmapData);
}
#endif

well that's about it, does anyone have any idea why everything is turning dark? p.s. : when i load another file that has a lot of different colors, you can barely see the image, and there are red, green, and blue stripes going across it which obviously means there is something a matter with my RGB values. does anyone know what this means? thanks for the help

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Usually the problem with this is the fact that the bitmap headers are not double word (32 bit) aligned, but most compilers make them 32 bit aligned. I had a serious problem with that in Borland C++ Builder for weeks until that was pointed out to me.

I don't know what compiler you're using, but it might do you good to write a simple program and check sizeof(BITMAPFILEHEADER). I believe it should be 14, not 16. However, if the code is copied directly from OpenGL Game Programming, then most likely that would be the problem. Hope you get it fixed!

EDIT: Changed sizeof(BITMAPINFOHEADER) to sizeof(BITMAPFILEHEADER).

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thanks for the help. i'm using Visual C++.NET version 2003. the code i'm using is for loading 24-bit bitmap files. i save the files as a 24-bit file, but it still doesn't work:-(

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I don't use MS Visual Studio, so I don't know how it operates. Is sizeof(BITMAPFILEHEADER)=14? If not, then you have to find a way to "pack" it. See, the bitmap header is as follows:


struct
{
char id[2];
int size;
short reserved[2];
int offset;
} BITMAPFILEHEADER;


More or less. It's implemented differently in Windows, but if you count it up, then it's 14 bytes. However, because projects in general are compiled for ease of the compiler, then it will be compiled using 16 bytes, with the last two (I think) being leftovers at the bottom of the structure. You have to overcome this, and since it's a compiler I can't use, I can't help you much more than that. So it all hinges on "what is sizeof(BITMAPFILEHEADER)?" ;)

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alright, i did as you said and you used the sizeof operator for use with BITMAPFILEHEADER struct. the output said that the BITMAPFILEHEADER struct is 14 bits. since it's 14 bits, what step should i take next?

thanks a bunch nychold:-)

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it's 14 bytes. I notice that you're not using glBindTexture in your DrawGround function to bind the texture. This is a potential (fairly likely in anything complicated) problem. Also, you may not have used glColor3f(1.0, 1.0, 1.0) to set the render color to white, which means it still may be some shade of dark green or something, which will mess up a lot of things.

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alright i changed the color value to glColor3f(1.0f,1.0f,1.0f); (or white in other words). This made my sand texture turn out the right way, but my scene is still darker than usual. any clue as to why?

thanks a bunch:-)

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